Studies of blood porphyrins in over 40 species will continue to include quantitative assays of total, free-, and zinc-complexed proto-and other porphyrins found in erythrocytes and/or in plasma. HPLC analysis of these porphyrins and of those found in urine and feces will be expanded, with special reference to the role of genetic factors, iron metabolism, and erythropoietic activity. Ferrochelatase and other enzyme activities will be studies in biopsies and cultured tissues of cattle with hereditary protoporphyria or erythropoietic ("congenital") porphyria. Unidentified fluorescing compounds found in a family with photosensitivity of unknown etiology and in serum of patients with renal disease will be characterized further after HPLC and other purification. Mechanisms of iron reduction and transport will be investigated in cultured bone marrow from selected human and animal subjects. Quantitative assays of heme in tissues and excreta will be expanded.